Liquid applicators are known which comprise a rotatably driven drum which is dipped into a pan of liquid, so that the liquid will be drawn from the pan and onto the surface of the drum as the drum is rotated. The liquid on the surface of the drum can be applied to the workpiece, merely by holding the workpiece against the drum surface as the drum is rotating. Such applicators have been used, for example, for applying wax to skis, and they have a variety of other uses.
Difficulties have been encountered in the past in providing a metering means for controlling the thickness of the liquid coating on the drum surface which, in turn, determines the thickness of the film to be applied to the workpiece. A usual expedient in the prior art has been to mount a knife-blade or bar on a stationary support adjacent to the drum and extending parallel to the axis of rotation of the drum, the knife-blade or bar being displaced a predetermined distance from the drum surface. However, for accurate control of the thickness of the liquid coating on the drum by such a means, especially when the thickness is relatively small, the drum must be manufactured to be exactly round within critical tolerances, and the drive for the drum must be accurately and precisely centered. Such requirements can be met only by extremely expensive machinery.
In accordance with the concept of the present invention, the metering rod rests on the surface of the drum itself, rather than being mounted on a stationary support independent of the drum. The spacing between the metering rod and the drum in the apparatus of the present invention is determined by shoulders formed on the rod itself, and this spacing is independent of irregularities in the roundness of the drum or misalignments in the drive of the drum since it follows the drum as it rotates.
In the practice of the present invention, the thickness of the liquid coating on the drum can be maintained uniform, even where extremely thin coatings are involved, and even though the roundness of the drum and the precision of its drive do not conform to strict tolerances. By means of the concept of the present invention, a thin liquid coating of a predetermined thickness can be maintained on the surface of the drum, even though the applicator itself is relatively inexpensive.
Different liquid thicknesses on the drum can be achieved, in the applicator of the present invention, merely by providing a plurality of the aforesaid metering rods having shoulders of varying diameters relative to the diameters of the rods themselves.